swift3:出直し。"fatal error: unexpectedly found nil while unwrapping an Optional value"が出ます。

書籍を購入してリストを入力したのですが、エラーが発生して動作しません。
大変申し訳ありませんが、どこが悪いのかご教授願います。

swift3
//
//  ViewController.swift
//  ICloudDemo
//
import UIKit

class ViewController: UIViewController{
    
    // Documentに関する情報
    struct USDocInfo {
        static let NAME = "usdoc_test"
        static let EXTENSION = "us"
        static var LOCAL_DOCUMENTS_PATH:String? = nil
        static var ICLOUD_CONTAINER_PATH:String? = nil
    }
    
    // アプリのサンドボックスのパスを格納する変数
    var localDocumentsPath: String {
        if let dir = USDocInfo.LOCAL_DOCUMENTS_PATH {
            return dir
        } else {
            let dir = NSSearchPathForDirectoriesInDomains(
                .documentDirectory,
                .userDomainMask,
                true)[0] + "/"
            
            USDocInfo.LOCAL_DOCUMENTS_PATH = dir
            return dir
        }
    }
    
    var iCloudContainerPath: String? {
        return USDocInfo.ICLOUD_CONTAINER_PATH
    }
    
    var document: USDocument!
    var documentURL: URL { return document.fileURL }
    var isFileExists = false
    
    let query = NSMetadataQuery()
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        query.searchScopes = [
            NSMetadataQueryUbiquitousDocumentsScope,
            NSMetadataQueryAccessibleUbiquitousExternalDocumentsScope]
        
        query.predicate = NSPredicate(format: "%K LIKE '*'", NSMetadataItemFSNameKey)
        
        DispatchQueue.global(qos: .default).async(execute: {
            if let url = FileManager.default.url(forUbiquityContainerIdentifier: nil) {
                print("iCloudコンテナのURL：\(url)")
                USDocInfo.ICLOUD_CONTAINER_PATH = url.path + "/Documents/"
                self.iCloudContainerDidInitialize()
            }
        })
    }
    
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        NotificationCenter.default.addObserver(self, selector: #selector(ViewController.iCloudDocumentDidChange(_:)), name: NSNotification.Name.UIDocumentStateChanged, object: self.document)
    }

    
    override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)
        NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIDocumentStateChanged, object: self.document)
    }
    
    
    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
    
    
    func iCloudContainerDidInitialize() {
        let filePath = iCloudContainerPath! + USDocInfo.NAME + "." + USDocInfo.EXTENSION
        let fileUrl = URL(fileURLWithPath: filePath)
        createDocument(fileUrl)
    }
    
    
    func createDocument(_ fileUrl: URL?) {
        
        let localFilePath = localDocumentsPath + USDocInfo.NAME + "." + USDocInfo.EXTENSION
        let localFileUrl = URL(fileURLWithPath : localFilePath)
        let doc = USDocument(fileURL : localFileUrl)
        
        doc.place = "自宅"
print("自宅")
        doc.save(to: localFileUrl, for: .forCreating, completionHandler: { (success:Bool) in
            //             "fatal error: unexpectedly found nil while unwrapping an Optional value"
print("pass")
            if success {
                print("Documentデータを保存しました。")
                
            } else {
                print("Documentデータを保存できませんでした。")
            }
            
        })
        
    }
    
    
    func iCloudDocumentDidChange(_ notification: Notification) {
        if self.document.documentState.contains(.inConflict){
            do{
                try NSFileVersion.removeOtherVersionsOfItem(at: self.document.fileURL)
            } catch let error {
                print("エラー内容:\(error)")
            }
            if let conflicts = NSFileVersion.unresolvedConflictVersionsOfItem(at: self.document.fileURL){
                for fileVersion in conflicts {
                    fileVersion.isResolved = true
                }
            }
        }
    }
}

もう一つのファイルです。

swift3
//
//  USDocument.swift
//  ICloudDemo
//

import UIKit

class USDocument: UIDocument {
    
    // Static定数の宣言
    struct USFileWrapperKeys {
        static let IMG = "USDocuemnt.img"
        static let PLACE = "USDocument.place"
        static let DATE = "USDocument.date"
        static let DETAIL = "USDocument.detail"
    }
    
    // 記録したい内容を保持するメンバ変数を宣言します
    var img:UIImage?
    var place:String?
    var date:Date?
    var detail:String?
    
    
    
    // 上記、Documentの内容をひとまとめにパッケージするNSFileWrapperもメンバ変数として宣言します
    var fileWrapper:FileWrapper?
    
    // MARK: - 書き込み用のメソッド
    
    override func contents(forType typeName: String) throws -> Any {
        
        if self.fileWrapper == nil {
            // 空のDictonaryを渡している
            self.fileWrapper = FileWrapper(directoryWithFileWrappers:[:])
        }
        
        if let place = self.place
            , let data = place.data(using: String.Encoding.utf8)
        {
            let fw = FileWrapper(regularFileWithContents:data)
            fw.preferredFilename = USFileWrapperKeys.PLACE
            self.fileWrapper?.addFileWrapper(fw)
        }
        
        if let img = self.img
            , let data = UIImageJPEGRepresentation(img, 1.0)
        {
            let fw = FileWrapper(regularFileWithContents:data)
            fw.preferredFilename = USFileWrapperKeys.IMG
            self.fileWrapper?.addFileWrapper(fw)
        }
        
        if let date = self.date {
            let data = NSKeyedArchiver.archivedData(withRootObject: date)
            let fw = FileWrapper(regularFileWithContents:data)
            fw.preferredFilename = USFileWrapperKeys.DATE
            self.fileWrapper?.addFileWrapper(fw)
        }
        
        if let detail = self.detail
            , let data = detail.data(using: String.Encoding.utf8)
        {
            let fw = FileWrapper(regularFileWithContents:data)
            fw.preferredFilename = USFileWrapperKeys.DETAIL
            self.fileWrapper?.addFileWrapper(fw)
        }
        
        return self.fileWrapper as Any
    }
    
}